JSON API: ReviewService.addFiles doesn't upload local files when specifying baseVersion

Hi,

I'm trying to upload a file to a review using the JSON API ReviewService.addFiles by sending a multi-part request.

I made the zip-archive with the MD5 named files.

It doesn't seem to work when I provide the baseVersion-field. I get a 200 OK response, but the file doesn't show up in the review.

Here's the request that *does* work (json part only):

[ {"command":"SessionService.authenticate"
  ,"args":{"login":"testuser","ticket":"da9606773eb579a5e554f7618522a068"}}
, {"command":"ReviewService.addFiles"
  ,"args":{"reviewId":33,"changelists":[{"zipName":"localFiles.zip"
                                        ,"versions":[{"md5":"887e24bfd1a53e8311d90a3cd3d3344e"
                                                     ,"localPath":"E:\\dev\\code\\github\\JavaTest\\pom.xml"
                                                     ,"action":"MODIFIED"
                                                     ,"source":"LOCAL"}]}]}}]

Here's the request that does *not* work (json part only):

[ {"command":"SessionService.authenticate"
  ,"args":{"login":"testuser","ticket":"da9606773eb579a5e554f7618522a068"}}
, {"command":"ReviewService.addFiles"
  ,"args":{"reviewId":34,"changelists":[{"zipName":"localFiles.zip"
                                        ,"versions":[{"md5":"887e24bfd1a53e8311d90a3cd3d3344e"
                                                     ,"localPath":"E:\\dev\\code\\github\\JavaTest\\pom.xml"
                                                     ,"action":"MODIFIED"
                                                     ,"source":"LOCAL"
                                                     ,"baseVersion":{"md5":"8eb41527a8f53e5d673771fa2159edac"
                                                                    ,"localPath":"E:\\dev\\code\\github\\JavaTest\\pom.xml"
                                                                    ,"action":"MODIFIED"
                                                                    ,"source":"LOCAL"}}]}]}}]

The only difference is that the latter request contains a baseVersion. I make sure I included both revisions in the zip-archive.

Any ideas on what I'm doing wrong here? (or where I could dig for some debug logging).